• The Transactions of The Korean Institute of Electrical Engineers
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• 제64권12호
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• pp.1730-1736
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• 2015

This paper presents a 16-channel transimpedance amplifier (TIA) array implemented in a standard $0.18-{\mu}m$ CMOS technology for the applications of panoramic scan LADAR (PSL) systems. Since this array is the front-end circuits of the PSL systems to recover three dimensional image for unmanned vehicles, low-noise and high-gain characteristics are necessary. Thus, we propose a voltage-mode inverter TIA (I-TIA) array in this paper, of which measured results demonstrate that each channel of the array achieves $82-dB{\Omega}$ transimpedance gain, 565-MHz bandwidth for 0.5-pF photodiode capacitance, 6.7-pA/sqrt(Hz) noise current spectral density, and 33.8-mW power dissipation from a single 1.8-V supply. The measured eye-diagrams of the array confirm wide and clear eye-openings up to 1.3-Gb/s operations. Also, the optical pulse measurements estimate that the proposed 16-channel TIA array chip can detect signals within 20 meters away from the laser source. The whole chip occupies the area of $5.0{\times}1.1mm^2$ including I/O pads. For comparison, a current-mode 16-channel TIA array is also realized in the same $0.18-{\mu}m$ CMOS technology, which exploits regulated-cascode (RGC) input configuration. Measurements reveal that the I-TIA array achieves superior performance in optical pulse measurements.

• Journal of Practical Agriculture & Fisheries Research
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• 제26권2호
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• pp.25-30
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• 2024

This study was conducted to develop the hanging type circular-patterned system that at maximizing the spatial efficiency of strawberry cultivation to increase yields, while also reducing labor and improving energy efficiency. The system consists of a cultivation bed units, longitudinal moving device, bed lifting device, front and rear transfer devices, lateral transfer device, nutrient supply device, and control unit. Performance testing revealed that the operational motor for longitudinal movement should have a torque of at least 0.1Nm based on the design weight and traction force of the cultivation bed unit. The power consumption required to move one cycle was calculated to be approximately 149Wh when performing harvesting or maintenance tasks for all 10 cultivation beds. Vibration angles measured during bed movement showed that the lateral transfer resulted in a roll angle ranging from -0.62° to 0.68° and a pitch angle ranging from -3.79° to 5.26°. For longitudinal transfer, the roll angle ranged from -3.37° to 3.36°, and the pitch angle ranged from -0.45° to 0.49°.

• Proceedings of the Korean Vacuum Society Conference
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.244.1-244.1
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• 2013

The p-type GaN which act as a hole injection layer in GaN-based LEDs has fundamental problems. The first one arises from the difficulty in growing a highly doped p-GaN (with a carrier concentration exceeding ~1018 $cm^{-3}$). And the second one is the absence of appropriate metals or conducting oxides having a work function that is larger than that of p-type GaN (7.5 eV). Moreover, the LED efficiency is decreases gradually as the injection current increases (the so-called 'efficiency droop' phenomenon). The efficiency droop phenomenon in InGaN quantum wells (QWs) has been a large obstacle that has hindered high-efficiency operation at high current density. In this study, we introduce the new approaches to improve the light-output power of LEDs by using graphene oxide sheets. Graphene oxide has many functional groups such as the oxygen epoxide, the hydroxyl, and the carboxyl groups. Due to nature of such functional groups, graphene oxide possess a lot of hole carriers. If graphene oxide combine with LED top surface, graphene oxide may supply hole carriers to p-type GaN layer which has relatively low free carrier concentration less than electron concentration in n-type GaN layer. To prove the enhancement factor of graphene oxide coated LEDs, we have investigated electrical and optical properties by using ultra-violet photo-excited spectroscopy, confocal scanning electroluminescence microscopy.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• 제15권6호
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• pp.181-186
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• 2015

With the rapid growth of semiconductor technologies, small-sized devices with powerful computing abilities are becoming a reality. As this environment has a limit on power supply, NVM storage that has a high density and low power consumption is preferred to HDD or SSD. However, legacy software layers optimized for HDDs should be revisited. Specifically, as storage performance approaches DRAM performance, existing I/O mechanisms and software configurations should be reassessed. This paper explores the challenges and implications of using NVM storage with a broad range of experiments. We measure the performance of a system with NVM storage emulated by DRAM with proper timing parameters and compare it with that of HDD storage environments under various configurations. Our experimental results show that even with storage as fast as DRAM, the performance gain is not large for read operations as current I/O mechanisms do a good job hiding the slow performance of HDD. To assess the potential benefit of fast storage media, we change various I/O configurations and perform experiments to quantify the effects of existing I/O mechanisms such as buffer caching, read-ahead, synchronous I/O, direct I/O, block I/O, and byte-addressable I/O on systems with NVM storage.

• Journal of the Institute of Convergence Signal Processing
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• 제25권1호
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• pp.46-51
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• 2024

Drone was first used for military purposes but as the range of use has recently expanded. It is being widely used in various industrial fields such as agriculture, service, logistics, and leisure. Lithium polymer batteries are lightweight and highly efficient, so they are mainly used as power supplies for drones. Accordingly, the need for lightweight and high energy density lithium polymer batteries has increased in order to supply stable power to drone. However, lithium polymer batteries can lead to ignition and explosion due to overcharging, short circuit, etc., so they must be used with a protective circuit installed. The protection circuit consists of a protection IC that monitors the voltage of the lithium polymer battery and a dual N-channel MOSFET that acts as a switch in case of overcharge and overdischarge. Therefore, this paper was implemented in one package form using a battery protection IC and a MOSFET semiconductor die chip serving as a switch. When implemented as a one chip package IC, at least 67% of savings compared to existing parts can be achieved.

• Proceedings of the Korean Vacuum Society Conference
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.237.2-237.2
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• 2013

ReRAM cell, also known as conductive bridging RAM (CBRAM), is a resistive switching memory based on non-volatile formation and dissolution of conductive filament in a solid electrolyte [1,2]. Especially, Chalcogenide-based ReRAM have become a promising candidate due to the simple structure, high density and low power operation than other types of ReRAM but the uniformity of switching parameter is undesirable. It is because diffusion of ions from anode to cathode in solid electrolyte layer is random [3]. That is to say, the formation of conductive filament is not go through the same paths in each switching cycle which is one of the major obstacles for performance improvement of ReRAM devices. Therefore, to control of nonuniform conductive filament formation is a key point to achieve a high performance ReRAM. In this paper, we demonstrated the enhanced repeatable bipolar resistive switching memory characteristics by spreading the Ag nanocrystals (Ag NCs) on amorphous GeSe layer compared to the conventional Ag/GeSe/Pt structure without Ag NCs. The Ag NCs and Ag top electrode act as a metal supply source of our devices. Excellent resistive switching memory characteristics were obtained and improvement of voltage distribution was achieved from the Al/Ag NCs/GeSe/Pt structure. At the same time, a stable DC endurance (>100 cycles) and an excellent data retention (>104 sec) properties was found from the Al/Ag NCs/GeSe/ Pt structured ReRAMs.

• Journal of Surface Science and Engineering
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• 제36권4호
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• pp.296-300
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• 2003

Extended cylindrical magnetron sputtering system with rotating 600-mm long and 90-mm diameter graphite cathode and pulsed power supply voltage generator were developed and fabricated. Time-dependent Langmuir probe characteristics as well as carbon films thickness were measured. It was shown that ratio of ions flux to carbon atoms flux for pulsed magnetron discharge mode was equal to $\Phi_{i}$ $\Phi$sub C/ = 0.2. It did not depend on the discharge current in the range of $I_{d}$ / = 10∼60 A since both the plasma density and the film deposition rate were found approximately proportional to the discharge current. In spite of this fact carbon film structure was found to be strongly dependent on the discharge current. Grain size increased from 100 nm at $I_{d}$ = 10∼20 A to 500 nm at $I_{d}$ = 40∼60 A. To deposit fine-grained hard nanocrystalline or amorphous carbon coating current regime with $I_{d}$ = 20 A was chosen. Pulsed negative bias voltage ($\tau$= 40 ${\mu}\textrm{s}$, $U_{b}$ = 0∼10 ㎸) synchronized with magnetron discharge pulses was applied to a substrate and voltage of $U_{b}$ = 3.4 ㎸ was shown to be optimum for a hard carbon film deposition. Lower voltages were not sufficient for amorphization of a growing graphite film, while higher voltages led to excessive ion bombardment and effects of recrystalization and graphitization.

• Journal of the Korean Society for Precision Engineering
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• 제31권11호
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• pp.993-998
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• 2014

Silver (Ag) grid patterned PET substrates were manufactured by thermal roll-imprinting methods. We coated highly conductive layer (HCL) as a supply electrode on the Ag grid patterned PET in the three kinds of conditions. One was no-HCL without conductive PEDOT:PSS on the Ag grid patterned PET substrate, another was thin-HCL coated with ~50 nm thickness of conductive PEDOT:PSS on the Ag grid PET, and the other was thick-HCL coated with ~95 nm thickness of conductive PEDOT:PSS. These three HCLs in order showed 73.8%, 71.9%, and 64.7% each in transmittance, while indicating $3.84{\Omega}/{\Box}$, $3.29{\Omega}/{\Box}$, and $2.65{\Omega}/{\Box}$ each in sheet resistance. Fabrication of organic solar cells (OSCs) with HCL Ag grid patterned PET substrates showed high power conversion efficiency (PCE) on the thin-HCL device. The thick-HCL device decreased efficiency due to low open circuit voltage ($V_{OC}$). And the Ag grid pattern device without HCL had the lowest energy efficiency caused by quite low short current density ($J_{SC}$).

• Journal of Microbiology and Biotechnology
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• 제16권12호
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• pp.1890-1896
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• 2006

Lumostatic operation for cultivation of Haematococcus pluvialis was assessed to test the scale-up strategy of photobioreactors. Lumostatic operation is a method of maintaining a proper light condition based on the specific light uptake rate ($q_e$), by cells. Lumostatic operations were performed in 0.4-, 2-, 10-, and 30-1 scale bubble column photobioreactors and the results were compared with cultures illuminated with constant light intensity. Significant differences were observed in the maximal cell concentrations obtained from 0.4-, 2-, 10-, and 30-1 scale photobioreactors under constant light intensity, yielding the maximal cell concentrations of $2.8{\times}10^5$, $2.2\times10^5$, $1.5\times10^5$, and $1.1\times10^5$ cells/ml, respectively. The maximal cell concentration in a 0.4-1 photobioreactor under lumostatic operation was $4.3\times10^5$ cells/ml. Furthermore, those in 2-, 10-, and 30-1 scale photobioreactors were about the same as that in the 0.4-1 photobioreactor. The results suggest that lumostatic operation with proper $q_e$ is a good strategy for increasing the cell growth of Haematococcus pluvialis compared with a constant supply of light energy. Therefore, lumostatic operation is not only an efficient way to achieve high cell density cultures with minimal power consumption in microalgal cultures but it is also a perfect parameter for the scale-up of photobioreactors.

• Journal of Dental Rehabilitation and Applied Science
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• 제21권1호
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• pp.33-42
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• 2005

This study was performed to investigate the surface properties and in vitro biocompatibility of electrochemically oxidized Ti-6Al-7Nb alloy by anodic spark discharge technique. Discs of Ti-6Al-7Nb alloy of 20 mm in diameter and 2 mm in thickness were polished sequentially from #300 to 1000 SiC paper, ultrasonically washed with acetone and distilled water for 5 min, and dried in an oven at $50^{\circ}C$ for 24 hours. Anodizing was performed using a regulated DC power supply. The applied voltages were given at 240, 280, 320, and 360 V and current density of $30mA/cm^2$. Hydrothermal treatment was conducted by high pressure steam at $300^{\circ}C$ for 2 hours using a autoclave. Samples were soaked in the Hanks' solution with pH 7.4 at $36.5^{\circ}C$ during 30 days. The results obtained were summarized as follows; 1. The oxide films were porous with pore size of $1{\sim}5{\mu}m$. The size of micropores increased with increasing the spark forming voltage. 2. The main crystal structure of the anodic oxide film was anatase type as analyzed with thin-film X-ray diffractometery. 3. Needle-like hydroxyapatite (HA) crystals were observed on anodic oxide films after hydrothermal treatment at $300^{\circ}C$ for 2 hours. The precipitation of HA crystals was accelerated with increasing the spark forming voltage. 4. The precipitation of the fine asperity-like HA crystals were observed after being immersed in Hanks' solution at $37^{\circ}C$. The precipitation of HA crystals was accelerated with increasing the spark forming voltage and the time of immersion in Hanks' solution. 5. The Ca/P ratio of the precipitated HA layer was equivalent to that of HA crystal as increasing the spark forming voltage and the time of immersion in Hanks' solution.